The invention generally relates to control of data communication between a data carrier and another device. More particularly, the invention relates to an electric circuit adapted to receive data in the form of data blocks, each data block including delimiter data and useful data, and which includes delimiter data detection means, adapted to detect delimiter data of a data block and to generate and to supply at least one useful data start signal, which at least one useful data start signal can be generated and supplied upon detection of the delimiter data, Such a data carrier and such a circuit have been developed by the applicant and have been put onto the market as an intelligent tag under the name “I•CODE” and are consequently known.
The known data stream has an interface for the contactless communication with an active write/read device. When the known data carrier comes within the communication range of the active write/read device an inductive coupling is established between the write/read device and the data carrier. The power for the operation of the electric circuit of the data carrier is then supplied to the data carrier with the aid of the interface and after an operating voltage has been built up a power-on reset signal is applied to the electric circuit. Furthermore, the data carrier receives a stream of data with the aid of the interface, said data taking the form of data blocks. The data blocks include delimiter data and useful data.
In order to enable the useful data to be utilized in the data carrier the data carrier should first be brought in synchronism with the stream of received data. For this purpose, the data carrier includes data carrier delimiter data detection means, which in an activated state are adapted to detect the delimiter data and to supply a useful data start signal upon such a detection. The delimiter data detection means can be activated by means of a start signal, which is formed by the power-on reset signal in the case of a first activation upon the entry of the data carrier into the communication range of a write/read device. After the detection of the delimiter data the useful data start signal is supplied, upon which the delimiter data detection means are deactivated. This ends a synchronization of the data carrier with the received data.
However, it is be ascertained yet that the synchronization was successful. For this purpose, the data carrier has a data test means adapted to receive the useful data start signal, testing of the received data for data errors being started upon reception of the useful data start signal. The data test means is adapted to supply a data error signal when a data error occurs. When a data error is found during testing of the received data the data test means generate and supply the data error signal and, subsequently, the data test means is deactivated. The presence of the data error signal can have different meanings. On the one hand, it can mean that a transmission error has occurred or that an instruction contained in the useful data is not supported. On the other hand, the occurrence of the data error signal may point towards an incorrect synchronization of the data carrier with the received stream of data.
In the present case, the data error signal forms the start signal for the delimiter data detection means regardless of the meaning of the data error signal, as a result of which the delimiter data detection means are reactivated and a detection of delimiter data is started again. Thus, synchronization of the data carrier is re-started.
In the case of the known data carrier the re-synchronization of the data carrier, which is still within the communication range, is repeated until the data test means no longer detect any data errors. When this situation occurs, i.e. when the data error signal does not appear, the data test means is adapted to supply the useful data to a useful data processing means, upon which the data test means is deactivated.
When in a communication protocol, which defines the time sequence of the stream of data and the contents of the delimiter data and the useful data of the data blocks, suitable measures are taken, such as an unambiguous distinction between the delimiter data and the useful data, i.e. when independence of the communication protocol of the useful data to be communicated is guaranteed, a simple and reliable synchronization of the known data carrier with the stream of data is possible within a foreseeable time interval that is acceptable for the use envisaged for the data carrier.
Even in cases in which there is no unambiguous distinction between the delimiter data and the useful data, i.e. the communication is not independent of useful data to be communicated, the provision of a data block pause between the data blocks which is longer than a maximum pulse spacing between pulses of the useful data also enables a reliable synchronization to be achieved, but this is at the expense of an undesired extension of the communication time.
When the known data carrier uses the communication protocol in accordance with the standard ISO/IEC FDIS 15693-2: 1999(E) for the communication, problems in the synchronization of the data carrier with the stream of data may arise because this communication protocol does not guarantee independence of the communication protocol of the useful data. This is because said standard provides for different delimiter data at the start of a data block (SOF delimiter data) and at the end of a data block (EOF delimiter data), the EOF delimiter data forming a subgroup of the SOF delimiter data. In connection with this communication protocol the problem may arise that with the known data carrier and the known circuit a combination of parts of the useful data adjoining the EOF delimiter data and parts of the EOF delimiter data are erroneously detected as SOF delimiter data, upon which the delimiter data detection means erroneously cause the data test means to start a test, which test inevitably ends up with a new synchronizing process. For two different codings of the data in accordance with the afore-mentioned standard at least 65 combinations may occur, for which in the worst case even no synchronization with the stream of received data is possible.